Method of making magnetic structures



Oct. 13, 1931.

[Mam/01,4 ifs/5mm (01/415) J. w. ANDREWS 1,826,711

METHOD OF MAKING MAGNETIC STRUCTURES Filed Aug. 24, 1929 fig fig ZCASE/A 2 DR) 2 4 a a /0 /2 A1 Patented Oct. l3, 1931 UNITED STATESPATENT OFFICE JOHN W. ANDREWS, OF CHICAGO, ILLINOIS, ASSIGNOR TO WESTERNELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OFNEW YORK METHOD OF MAKING MAGNETIC STRUCTURES Application filed August24, 1929. Serial No. 388,082.

This invention relates to a method of making magnetic structures, andmore particularly to a method of producing magnetic cores of acompressed dust typefor use in telephonic communicating systems.

The principal object of the invention is to provide a method ofproducing magnetic structures having low core losses and a relativelyhigh permeability to'enable a given 1nductance to be obtained from ammimum amount of material and possessing to a. high degree thoseelectrical and magnetic characteristics which make it highly desirablefor use in electrical signaling apparatus, particularly in loading coilsfor telephone circuits.

One embodiment of the invention contemplates the construction ofmagnetic cores for loading coils of nickel-iron alloys in finely dividedform having higher inherent magnetic permeability and lower inherenthysteresis loss than iron. These properties are obtained by treatingmetal or alloy particles with certain organic materials which uponheating disintegrate, passing through a gradual and continuoustransition from a gummy substance to a solid to form an insulating icoating thereon after which the insulated particles are compressed intocores of any desired shape and size. The cores are then heat treated atthe optimum temperature for the particular alloy of which the cores areconstructed to stabilize the insulator and to 've a high permeabilityand low hysteresis oss.

Other features and advantages of the invention will become apparent fromthe following detailed description of one embodiment thereof, referencebeing had to the accompanying drawings, wherein Fig. 1 is a perspectiveview of a section'of an inductance loading core made in accordance withthe present invention, and Fig. 2 shows a' curve illustrating theinsulative resistances obtainable with various organic insulatingmaterials.

' It will be understood, however, that Fig. 1 is merely illustrative andthe invention 1s not limited to' the production of this form of core,but is adapted to the production of magnetic parts of various forms.

'centages of nickel and iron.

In practicing the present invention, the magnetic material is preferablyprepared from brittle alloys containing various per- These alloys arerepared as fully described in the patent to P. Beath and H. M. E.Heinicke, No. 1,669,649 issued May 15, 1929. The preferred form of thealloy, commonly referred to as permalloy,is prepared by meltingapproximately 81 parts of nickel and 19 parts of iron in an oxidizingatmosphere and pouring the resulting alloy into a mold.

An alloy thus prepared is rolled while hot into relatively thin slabsand quenched to produce a fine crystalline structure which is verydesirable since the disintegration of the material takes place at thecrystal boundaries, and consequently the smaller size of the crystals,the finer the dust which can be produced from the finished product. Themagnetic alloy thus received in slab form is reduced to a finely dividedform or dust, in any well known manner; as for example, in a hammer millor other suitable reducin apparatus, and subsequently pulverized 1n anattrition or ball mill.

The dust from the attrition mill is sieved and the portionpassing-through a 120 mesh sieve is placed in a closed-container andannealed at a temperature of approximately 885 C. The annealed dust isremoved from the container in the form of a cake which is again reducedto a powder by crushing in a rotary crusher and subsequently grinding inan attrition mill. The sieved through a standard 120' mesh screen andthe dust passing through such a screen is insulated with an organicinsulator.

According to one 'form of the invention,

the insulator for the dust particles is pre-v pared by mixing'theingredients in approximately the following proportions: I

- 1 partof lue orsoap 80 partso water. i The metallic dust is thoroughlymixed with the solution, the amount of the metallic dust added beingdetermined by the permeability desired and the particular useito whichthe finished cores are to be put. The entire mass ground dust is again vis then boiled to a predetermined degree of dryness as determined by thepoint at which maximum resistance is obtainable for the particularorganic substance being used, accompanied by constant stirring toprevent caking and to insure a thorough coating of the individual dustparticles. 7

The insulated dust is sieved through a 16 mesh screen and placed in amold and compressed into core parts under a pressure of approximately200,000 pounds per square inch. The core parts are then transferred toan annealing furnace where they are annealed at the optimum annealingtemperature of approximately 500 C. and cooled. The core parts are thendipped in shellac to give them a moisture proof coating.

A plurality of core parts thus formed are then stacked co-axially toform a core on which the usual toroidal winding is applied, the numberof such parts used depending upon the existing electricalcharacteristics of the telephone circuit with which the loading coilsare to be associated.

As indicated by the graphical representation of Fig. 2 the time ofdrying of the dust being lnsulated is controlled by the particularorganic insulating material used and the maximum resistance obtainable.By the term dry as used with reference to that point on the curve ismeant'that degree of dryness when the insulated dust rolls freely from apolished metallic'surface. As illustrated by the curves of Fig. 2, themaximum resistance obtainable with soap or casein occurs substantiallyat the dry point just described. Whereas with the use of glue as theinsulator, the maximum resistance occurs when the time of heating iscarried approximately 6% minutes beyond the dry point, terminating at atemperature of approximately 200 C. The underlying principle of thesuccess of an organic material as an insulator is that the material uponheating disintegrates, passing through a gradual .and continuoustransition from a gummy substance to a brittle solid to provideinsulation between the metallic particles.

Casein as an insulator for the dust particles is prepared by thoroughlymixing one part of casein with ten parts of water. For example, skimmilk has been found to give satisfactory results.

Although the metallic dust has been described as being insulated with asolution of glue, casein. soap or milk in definite proportions, it is ofcourse to be understood that the proportions of the differentingredients may be varied without departing from the spirit and scope ofthe invention. Also. other organic materials such as colloidalnitrogenous substances. sugars, refinery syrups. starches. and dextrinmay be successfully used. It will also be understood that the organicinsulators are not confined to aqueous solutions since heating to forman insulating solid, heating the coated particles to cause the organicmaterial to disintegrate to form an insulating solid, and forming a massof the insulated particles into a homogeneous structure.

3. The method of making magnetic structures composed of an alloy, whichconsists in reducing the alloy to finely divided particles, coating theparticles with an organic insulating material which disintegrates uponheating to form a solid, and forming a mass of the insulated particlesinto a homogeneous structure.

4. The method of making magnetic structures, which consists in reducingan alloy to line particles, heat treating the particles, re-

ducing the product so obtained to dust, coating the dust uniformlythroughout with an organic material which disintegrates upon heating toform an insulating solid, and forming a mass of the insulated dust intoa. homogeneous structure.

5. The method of making magnetic structures, which consists of mixingparticles of magnetic material with a solution of organic materialadapted to disintegrate and form an insulating solid, heating themixture to cause the organic material to disintegrate and form aninsulating solid over each particle. and forming a mass of the insulatedparticles into a homogeneous structure.

6. The method of making magnetic structures, which consists in mixingparticles of a magnetic material with a solution of organic materialadapted to disintegrate and form an insulating solid, heating themixture to cause the organic material to disintegrate and form aninsulating solid over each particle, forming a mass of the insulatedparticles into a homogeneous structure, and heat treating the structure.

7. The method of making magnetic structures. which consists inreducingan alloy to finely divided particles, coating the particles withan organic insulating material which disintegrates upon heating to forma solid, forming a mass of insulated particles into a homogeneousstructure, and heat treating the structure to a temperature ofapproximately 500 C. 1

8. The method of making magnetic structures, which consists in mixingparticles of a magnetic material with a solution of organic materialwhich disintegrates upon heating to form an insulating solid, forming amass of the insulated particles into a homogeneous structure, and heattreating the structure at an optimum temperature determined by the pointof minimum loss.

9. The method of making magnetic structures, which consists of mixingnickel-iron particles with a solution of organic material whichdisintegrates upon heating to form an insulating solid, compressing amass of the 16 insulated particles into a homogeneous structure, andheat treating the structure at an' optimum temperature determined by thepoint of minimum loss.

10. The method of making magnetic struc- 20 tures composed of an alloyof not more than nickel and the remainder principally iron, whichconsists in reducing the alloy to finely divided particles, mixing theparticles with organic material adapted to disintegrate and form aninsulating solid, simultaneously heating and stirring the mixture tocause the organic material to disintegrate and form an insulating solidover each particle, and forming a mass of the insulated dust into ahomogeneous structure.

11. The method of making magnetic structures composed of a ferrousmagnetic alloy containing 81% nickel, which consists of coatingparticles of the alloy with an organic material which disintegrates uponheating to form an insulating solid, and forming a mass of the insulatedparticles into a homogeneous structure.

12. The method of making magnetic structures, which consists in mixingparticles of a magnetic material with a solution of a colloidal organicsubstance which disintegrates upon heating to form an insulating solid,

simultaneously heating and stirring the mix- 48 ture to form aninsulating solid over each of the particles, and forming a mass of theinsulated particles into a homogeneous structure.

13. The method of making magnetic struc 50' tures, which consists inmixing particles of a magnetic material with a solution of glue,

simultaneously heating and stirring the mixture to cause the glue todisintegrate and pass through a gradual and continuous transition I.from a gummy substance to a solid to form an insulating coating overeach of the particles, and forming a mass of the insulated particlesinto a homogeneous structure.

14. The method of making magnetic structures, which consists in mixingparticles of a magnetic material with an organic material,

heating the material to effect its disintegration and gradual andcontinuous transition from a gummy substance to a solid to form 06 aninsulating coating on the magnetic particles, and forming a mass of theinsulated particles into a homogeneous structure.

15. The method of making magnetic structures, which consists in coatingparticles of a magnetic material with casein which disintegratcs uponheating to form an insulating solid, and forming a mass of the thusinsulated particles into a homogeneous structure.

In witness whereof, I hereunto subscribe my name this 15th day ofAugust, A. D. 1929.

JOHN W. ANDREWS.

